Adam --

You're right (and that was a perceptive question!). The comma is used in a nonstandard way. A bit of background:

The clause beginning "It is important" is independent and the one beginning "because" is dependent. But the rule that applies here isn't whether the clause is independent or dependent. It’s whether the “because” clause is essential or inessential to the meaning of the sentence.

Here’s the explanation from the Modern Language Association (a style god for writers of theses, dissertations, and other academic works):

“When the main clause of a sentence contains a positive verb, inserting a comma before because makes what follows nonessential to the meaning of the sentence: Alex ordered the book online. Robert also ordered the book online, because he was running out of reading material.”

So you if see the dependent “because” clause as essential, you’re right. The sentence doesn’t need a comma. The same applies to the “without it” phrase.

The problem, as you say, is that the sentence would be long-winded without a comma. But by putting commas before “because” or around “without it,” you’d be making them inessential to the sentence. So I’m seeing a lot of the kind of improvised just-one-comma construction you noticed.

It doesn't really make sense. But the rule seems to be in flux, and if I were editing a manuscript with that construction, I’d probably go with the author’s preference. Thanks for asking a question that was fun to answer :).

Jan